Multiphase DC/DC converters have gained a significant market share in high current low output voltage applications. Conventional converters include an integrated pulse width modulation (PWM) controller, power MOSFETs and an output filter, such as that shown in the FIG. 1, in which power conversion is performed by a plurality of power channels working in parallel. An output filter typically includes inductors (L) and capacitors (C). The MOSFETs control current in the output inductors in which a high-side switch selectively couples the inductor to a positive power supply while a low-side switch selectively couples the inductor to ground. The PWM controller controls the high-side and low-side switches. An important function of the PWM controller is to assure equal sharing between the plurality of channels and provide protection functions to the MOSFETs. Conventional current sharing functions include sensing channel current (typically via sensor circuitry such as the resistors shown in FIG. 1), comparing channel currents to the average system current, and adjusting control signals of the PWM controller in accordance with the results. The sensed channel current information can also be used to monitor the state of a load.
Components of the current sensing circuitry, are typically not integrated with the PWM controller and thus are susceptible to damage or variations from manufacturing, testing, and operation. For example, current sense resistors or printed wires can be damaged during the processes of placing, soldering, washing, and handling at manufacturing, or burned out due to a severe overload. In any of these cases the channel current information (typically produced in the form of a representative signal) obtained from the current sense resistor will not be a true representation or is not produced at all, falsely indicating a zero current.
Conventional current share schemes will respond to such a false zero current indication by steering more current to that channel creating a severe overload for the components within this channel. An example of a behavioral pattern of a four-channel system with a failure in the second channel current sense path is illustrated in the graph shown in FIG. 1A. As shown in the graph, most of the load current, approximately 60A, has been steered into the second channel. Eventually, the overall system will encounter catastrophic damage as a single channel of a multiphase system is typically designed to carry a load that is only 1/n of the system load. Therefore, a need exist for a effective approach for detecting sensing component irregularity or failure for improving overall system reliability and robustness and/or increasing manufacturing yields.